Furnace



Sept 25, 1945- c. P. CLAPP ETAL 2,385,333

FURNACE Filed Feb. 2, 1942 ,Z1 TZ 3.91

Patented SeptQZS, 1945 Channing P. Clapp,

Fords, and Boyd M. Johnson,

Metuchen, N. J., asslgnors to The Carborundum Company, Niagara ofDelaware Falls, N. Y., a corporation Application February 2, 1942,Serial No. 429,219

l1 Claims.

The invention of this application relates to improvements in the'construction and operation of furnaces, particularly ofA furnaces usedfor the melting of metals and especially nonferrous metals such asaluminum or other substances having a relatively low absorptivty ofrasant neat.

The primary object of this invention is to provide a method whereby theeectlve rate of heat delivery in furnaces to substances of the classabove referred te, may be increased. Other objects are to protect thesurface of the molten mass in the furnace from contact with theatmosphere of the furnace and to produce a more uniform heating of thebath in the furnace.

The drst of the above-mentioned objects can be accomplished by coveringthe surface of the molten material in the furnace with a cover of amaterial whose properties include high absorptivitv for radiant heat,the lack of any appreciable tendency to react with the molten bath erheating gases, and high thermal conductivity.

in the drawing, Figure 1 is a longitudinal sectional view. taken on Linel--l of Figure 2, of a furnace embodying the improvements of the invention. Figure 2 is a sectional View taken on line t--t of Figure 1.Figure 3 is a sectional View similar to Figurez but showing a modifiedheating arrangement and a. mule arch.

The present invention as applied to a furnace will be more readilyunderstood from the-following description in which reference is made tothe drawing. Shown in Figure l is a typical metal melting furnace l inwhich an insulating housing 2 lined with refractory material 3 forms achamber t adapted to contain molten metal. Access to the chamber 4isgained through refractory lined passage or charging space 5 into whichmetal may be charged in suitable form. A forehearth 6 is provided fromwhich molten metal may be withdrawn.

A combustion chamber l, also linedwith refractory. material and heated-by burners ll, is provided over molten metal receiving chamber 4. liutochamber l through passages 8 additional products of combustion fromsuitable burners 8^ or het gases from other heating sources are directedand from this chamber all products of combastion pass out through one ormore vents or nues 9, preferably located at the charging end of thefurnace to provide for preheating of the cold incoming metal.

Metals generally and especially molten metals are outstanding examplesof substances having low radiant heat absorptivity, the absorptivity ofadapted to float on.

as to prevent as far as possible,

metals such as aluminumy copper, zinc and their alloys being .3 or loweras compared to the 1.0 of a theoretical black body. In a furnace of thetype described, therefore, it is desirable to have in contact with thesurface of the metal, a cover of a material vsuch as htherto discussed,which has a high absorptivity for radiant heat. This is provided in theillustrated furnace by tiles l5, provided with opstanding peripheraledges lli, the surface of the molten metal in chamber Il and being soconstructed as to lit together and against the walls of the furnacechamber i with only small clearances so exposure of the atmosphere.Refracbe provided to prevent the event the molten metal to the furnacegas tory stops or rests l1 may displacement of the tiles in .metal levelfalls unduly.4

Tiles l5 are preferably madey of bonded silicon carbide, though lothermaterials such as graphite and in some cases solid metals of suitablemelt ing point and having surfaces with a high absorptivty for radiantheat may also be used. The peripheral opstanding rims I5 on tiles l5 arenot under all conditions necessary, since, where the specific gravity ofthe tiles is less than that of the molten metal they will float on thesurface of the metal without being rimmed. It will be realized that thetiles l5 must have a. comparatively high heat-conductivity and must, inoperation, have good contact with the molten metal over a large `area inorder to operate eliiciently.

In some cases thin granular layers or dispersed granules of materialshaving a high absorptivity for radiant heat may be used instead of thesolid tile. Among the granular materials which may be useful for thispurpose are silicon carbide, graphite, fused alumina, chromite ore andilmenite. All of these substances have an absorptivlty of radiant heatapproaching that of a black body, that is of about .9. Where a blanketor layer of granular material is used on the surface of the material orin other operations where it is desired to avoid all contact of oxygenor ue gases with the surface of the metal being melted, it may benecessary to provide a neutral or re'- ducing atmosphereabovethegranular layer or tile covering the surface of the metal. In suchcases a mule may beprovided as shown in Fig. 3 where an arch 3D ofsuitable refractory material rests on the refractory side walls of thefurnace. In the operation of this construction the arch 30 is heated bythe products of combustion in combustion chamber 1, tile l5 is heated byra- Figures 1 and 2 metal pigs are structed that U shaped passages Q2are formed therein, which passages connect at one end through ports I3with combustion chamber l. In Figures l and 2 the products of combustionfrom burne s 8' pass down through passages il,

the U-shaped passages d2 in tiles it and out through ports i3 intocombustion chamber l.

From chamber l products of combustion escape through flue or ues 9.

In Figure 3 a somewhat different arrangement is shown, the combustiongases beingintroduced into the combustion chamber 'l through passages orburners 8a and passing from chamber i via ports i3 through U-shapedpassages d2 in tiles l0 to the atmosphere through flues 9a. It isdesirableyin thev construction shown in Figure 3, to also include one ormore ues ii at the end of combustion chamber 'l through swhich, ifdesired, some or alll of the gases may 'be dischargedwithout passingbelow the level of the metal bath. The provision of flue or ues 9 forauxiliary or alternative use is important since in the event of stoppageor blocking of the U-shaped passages 132 the exhaust of combustion gasesfrom chamber 'l would not be interrupted.

As shown in the drawing, tiles 40 are so con 'structed that the openingsof passages 42 are above the surface of the metal bath, thus preventingthe loss of metal which would result if the openings Werebelow thesurface-of the bath and on'e or more of the tiles should crack. Thus,even if all of tile 430 should crack on their sides in contact with thebath or become otherwise stopped up, the furnace still could be operatedin an emergency, though of course at a reduced eflciency and rate ofoutput.

It will be understood that the heat-absorptive covering may be used forincreasing heating emciency without the use of hollow tile dll, or viceversa. However, the use of the tiles 4 0 lis desirable not only from thestandpoint of the increased heating surface for ,the metal thusprovided, but also because they allow the appplication of heat near thebottom of the bath,`

thereby promoting circulation of the molten metal and consequently more,uniform heating and more rapid heat transfer. When heat is applied onlyto the top of the bath vthere is a tendency for the metal near the topto remain considerably hotter than the lower part of `the bath becauseof the lower density of the hotter metal. Consequently, with top heatingalone the only means of bringing the lower portions of the bath up tothe desired temperature is by conduction through the molten metalitself. While in some cases this is satisfactory, with metals havingrelatively low heat conductivity such as molten'aluminum a greatimprovement in the ra'te of heating is obtained by the use .of'submerged heating units" such as tiles 40.

During the operation of the furnace shown in fed into the furnacethrough chargingspace 5 and may be preby combustion gases from betweensaid heated while lying on the floor l0 thereof by radiation-^ from therefractory wall II of flue 9. After preheating, the metal pigs aredropped into the bath of molten metal contained in chamber 4 where they,too, become molten. Molten metal as desired for casting or otherpurposes may be dipped or otherwise removed from forehearth 6.

The molten metal in chamber 4 is heated by conduction from refractorytiles I5 in contact .with the metal, and from the Walls of hollowtiles'dll. Both tiles l5 and 40 are heated directly burners 8 and/or illand in addition tiles i5 are heated by radiation from the refractorylining 3 of combustion chamber 'l since lining 3 is Well insulated byinsulation i2 and will therefore be at a somewhat higher temperaturethantiles i5 which yare in contact with conduction. r

The operation of the modiied furnace shown in Figure 3 is essentiallythe same as above described but here the tiles i5 are heated byradiation from mufiie arch 30 which in turn is heated by the combustiongases in chamber l. While the invention of this application has beenparticularly described in connection with one type of furnace it will beunderstood that the principles of the invention can be applied tofurnaces of other thereof may be obtained with many variations inconstruction which will be suggested by the the metal and thus lose heatby .foregoing descriptio Having thus described our invention we do notkwish to be limited by the details in the description but only by thescope of the following claims.

We claim:

1. A metal-melting furnace comprising: a housing; a combustionchamber insaid housing; at lea'st one inlet and at least one outlet for saidcombustion chamber; a heating chamber in said an inlet and an outlet forsaid heating Vclaim 1 in which a muiile. arch supported by the sidewalls of said heating chamber is interposed combustion chamber and saidheatconductive refractory wall.

3. A metal-melting furnace comprising: a housing; a combustion chamberin the upper po tion of said housing; a plurality of inlets and at leastone outlet for said combustion chamber; a heating chamber in saidhousing; an inlet and an outlet for said heating chamber; a wall ofheat-conductive refractory material separating said heating chamber andsaid combustion chamber; said Wall comprising tiles formed of a materialhaving a high coefi'icivent of absorptivity'for radiant heat and beingadapted to float upon molten metal contained in said heating chamber.

4. A metal-melting furnace comprising: a housing; a combustion chamberin said housing; inlets and at least one outlet for said combustionchamber; a heating chamber in said housing; an inlet and an outlet forsaid heating chamber;

types and the advantages of a bath of molten float on molten metalcontained in said heating chamber.

v 5. A metal-melting furnace comprising: a housing; a combustion chamberin said housing; at least one inlet and at least one outlet for saidcombustion chamber; a heating chamber in said housing; an inlet and anoutlet for said heating chamber; heat-conductive refractory hollow tilesforming at least a portion of the wall of said heating chamber, saidhollow tiles having U-shaped passages therein adapted to conduct heatinggases whereby heat is transferred to said heating chamber.

6. A metal-melting furnace comprising: a housing; a combustion chamberin said housing; a plurality of inlets and at least one outlet for saidcombustion chamber; a heating chamber in said housing; an inlet andanoutlet for said heating chamber; heat-conductive refractory hollowtiles forming at least a portion of the wall of said heating chamber,said hollow tiles having U-shaped passages therein adapted to conductheating gases whereby heat is transferred to said heating chamber, andthe ends of said U-shaped passages .being so located as to be above thelevel metal contained in said heating chamber.

7. A metal-melting furnace as set forth in claim 6 in which a muiiiearch supported by the side walls of said heating chamber is interposedbetween said combustion chamber and said heating chamber.

8. A metal-melting furnace comprising: a housing; a combustion chamberin said housing; inlets and outlets for said combustion chamber; aheating chamber in said housing; an inlet and an outlet for said heatingchamber; heat-conductive refractory hollow tiles *formingy at least aportion of the wall of said heating chamber; said hollow tiles havingU-shaped passages therein; a heat-conductive refractory wal separatingsaid heating chamber and said combustion chamber; said refractory wallcomprising tile of a material having a high eoeiilcient of absorptivityfor radiant heat and being adapted to float on molten metal contained insaid heating chamber; said U-shaped passages communicating at one endwith said combustion chamber and at the other end with the exterior ofsaid housing; whereby molten metal in said heating chamber will beheated by conduction from said tiles.

9. A metal-melting furnace comprising: a

housing; a combustion chamber in said housing;

5 inlets and at least one outlet for said combustion chamber; a heatingchamber in said housing; an

inlet and an outlet for said .heating chamber; a

heat-conductive refractory wall separating said heating chamber and saidcombustion chamber; said refractory wall comprising tile of a materialhaving a high coefficient of absorptivity for radiant heat and beingadapted to oat on molten metaloontained in said heating chamber;heatconductive refractory hollow tiles forming at least a portion of thewall of said heating chamber and containing U-shaped passages therein;said passages communicating at one end with said combustion chamber andat the other end with a source of heating gases; whereby molten metal insaid heating chamber will be heated by conduction from said til l0. Ametal-melting furnace as set forth in claim 9 in which a muilie archsupported by the side walls of the heating chamber is interposed betweensaid combustion chamber and said heatconductive refractory wall.

1l. A metal-melting furnace comprising: a housing; a combustion chamberin said housing; inlets and at least one outlet for said combustion sochamber; a heating chamber in said housing; an inlet and an outlet forsaid heating chamber; a heat-conductive refractory wall separating saidheating chamber and said combustion chamber; said refractory wallcomprising tile of a material having a high coemcient of absorptivityfor radiant heat and being adapted to float on metal contained in saidheating chamber; heatconductive refractory hollow tiles forming at leasta portion of the wall of said heating chamber and 40 containing U-shapedpassages therein; said passages communicating at one end with saidcombustion chamber and at the other end with a source of heating gases;the ends of said iJ-shaped passages being located above the level of themolten metal bath contained in said heating chamber.

CHANNING P. CLAPP. BOYD M. JOHNSON.

molten

